A variety of unsymmetrically substituted alkyl 3-alkoxypropionates can be prepared by transesterification of identically substituted alkyl 3-alkoxypropionates. Unfortunately, the terminal alkyl moieties tend to scramble when known transesterification catalysts such alkali metal alkoxides, sulfuric acid and the like are used, apparently by promoting the reverse Michael reaction of the alkyl 3-alkoxypropionates. In addition, such catalysts produce other undesirable side products, presumably derived from the products of the reverse Michael reaction of the alkyl 3-alkoxypropionates. Other catalysts known to have transesterification activity do not produce by-products-because they are essentially unreactive with the alkoxyesters employed in the practice of the present invention. Thus, neither transesterification nor by-product formation occurs.
U.S. Pat. No. 4,614,613 (assigned to BASF Aktiengesellschaft) discloses the use of titanium (IV) or tin (IV) compounds which are soluble in organic medium for the transesterification of .beta.-N-aziridinopropionates of lower alcohols with relatively high boiling alcohols or polyalcohols. This reference is specific to the transesterification of .beta.-N-aziridinopropionates and addresses the problem of side reactions such as polymerization of the three-membered aziridine ring.
The specific compounds which are the subject of the '613 disclosure are subject to many side reactions and process constraints as a result of the presence of the aziridino moiety as part of the reactive molecule. The mono- and polymeric secondary and tertiary amine species present in the '613 reaction system are capable of interacting with the titanium and/or tin catalyst, thereby aiding the promotion of the desired reaction.